As functions of recent mobile terminals improve such as notebook personal computers, mobile phones, PDA (Personal Digital Assistant) and game consoles, there is an increasing need for, in the course of use of various kinds of on-line services such as Web and on-line game on terminals including a desktop personal computer, a television set and a car navigation system, transferring service to another terminal (e.g. mobile terminal) as required to continuously use the service on the terminal as the transferring destination. Possible is, for example, transferring service to a cellular phone while on-line shop is used on a Web by a desktop personal computer.
For realizing such processing, it is a common practice to incorporate a function for service transferring (service transferring function) into an individual service application on a server which provides service. Description will be made, for example, of a case where a user using on-line shop by a personal computer halfway starts continuous use of the service on a cellular phone.
For thus enabling a user who uses on-line shop by a personal computer to halfway start continuous use of the service by a cellular phone, a service temporary interruption function and a use resuming function as a service transferring function are mounted on a Web site (service application) which provides on-line shop service.
When a user selects the temporary interruption function during the use of service by the personal computer, information indicative of a state of the service being used (session information) is stored on a server side. In this state, when the user successively accesses a Web site for cellular phone by using a cellular phone as a service transferring destination to execute user authentication and further selects the use resuming function, the use can be resumed from a state of temporary interruption by restoring the session information of the service which is stored before on the server side.
Disclosed in Patent Literature 1 is a method of a server client system in which data held by a client terminal is transferred to other terminal as it is, so that a terminal as a transferring destination takes over a state of a client application as of before switching and receives service from a server.
The method recited in Patent Literature 1 enables continuous use of service by transferring information indicative of a state of service being used on a terminal as a transferring source (session information) to other terminal as a transferring destination to restore the session information interrupted on the transferring destination terminal.
Disclosed in Patent Literature 2 is a method which realizes service transfer between terminals with a special gateway provided between a server and a terminal. In this method, the gateway manages session information between the server and the terminal, based on which information, communication between the server and the terminal is appropriately switched to realize service transfer between the terminals.    Patent Literature 1: Japanese Patent Laying-Open No. 2007-140712    Patent Literature 2: Japanese Patent Laying-Open No. 2002-176432
When a plurality of services independent from each other which are provided by a plurality of service providers are used on one terminal and transferred to another terminal, however, there are the following problems.
First problem is that when transferring service between terminals by using such a service transferring function as described above which is incorporated into a service application, operation will be extremely complicated for a user. The reason is that with a service transferring function provided for each service application, even when transferring operation is executed in any one of service applications, none of its information is shared by other service applications, so that the transferring operation should be repeatedly executed for each service used by the user.
Another problem is a large development burden for a service provider. The reason is that the service transferring function should be incorporated into each service application.
Second problem is that when information indicative of a state of service being used on a terminal as a transferring source (session information) is directly transferred to other terminal as a transferring destination, service security might not be maintained by the method recited in Patent Literature 1. The reason is that only the transfer of session information between terminals enables service switching, which prevents a server (service application) side from recognizing service transfer of the terminals. It might happen, for example, that by copying session information of service being used by a certain user onto other terminal by using wireless communication such as wireless LAN or infrared communication by a third party, he or she uses the service as it is.
Third problem is that in such a case where a network between the server and the terminal is under the management of a communication service provider as in a case of a cellular phone network, service transfer cannot be realized by such a method which realizes transfer of service between terminals with a special gateway provided between a server and a terminal as recited in Patent Literature 2. The reason is that when the network is under the management of a service communication provider, neither a terminal user nor a service provider is allowed to dispose a gateway between a server and a terminal.
The method recited in Patent Literature 2 has a further problem that no transfer of service can be realized in such a case where a plurality of terminals are connected to different networks as a cellular phone and a personal computer. The reason is that it is difficult to dispose a common gateway between a plurality of terminals connected to different networks and a plurality of servers.
In addition, when a special gateway is provided for realizing transfer between terminals in a wide area network, a bottleneck might occur on communication. The reason is that all the communication between servers and terminals pass through the gateway.